Classic Hifi Care

Love V-M equipment. Stylish, charming and easy to work on. These are my 2 restored sets from 1960.

Are they both PP?

Bill

William wrote: ↑Mon Jul 31, 2023 11:55 am Are they both PP?

Bill

Yeah push pull 6V6 with 12AX7 pre amp

I never have been able to figure out which VM has PP or is single ended without seeing it or a schematic. All of my VM consoles are 6BQ5 PP. Is a VM 1000 on your wish list?

Bill

William wrote: ↑Mon Jul 31, 2023 12:23 pm I never have been able to figure out which VM has PP or is single ended without seeing it or a schematic. All of my VM consoles are 6BQ5 PP. Is a VM 1000 on your wish list?

Bill

No, because it's too big and heavy. Mine both use this amp

I wish I had one of those amps and the control/preamp part that goes with it. I picked up a VM console for ten buck a few years ago. The amp and control/preamp were missing so all I got was the speakers and changer. I can see in the bottom of the cabinet an outline where the amp was located. I'm surprised the cabinet did not end up in a dumpster.

Bill

I'm looking at one of those amps, stereo PP 6V6 in the coming weeks. I saw a SE 6BQ5 from an 853, I like how these are put together.

Sticky tile floor and dark wood paneling... so '60s! A perfect match for these early '60s consoles.
I had a '62? VM console that had separate preamp/control and a PP 6BQ5 amp, a nice unit., though the speaker complement was rather ordinary: 12" woofer and cone mids and tweeters, and a VM 1200 with ceramic cart. Sounded OK.

Motorola minion wrote: ↑Tue Aug 01, 2023 10:05 pm I'm looking at one of those amps, stereo PP 6V6 in the coming weeks. I saw a SE 6BQ5 from an 853, I like how these are put together.

The amplifier chassis came in the mail last week. I pulled the sams schematic for this amp, which may need a power transformer. The donor chassis would be a Motorola HS-793, famously used in the first series of 3-channel consoles.
That amp came from an SK29 after I swapped in a chassis that was a spare I had forever. Now that the OPTs are all gone to fix other equipment, there is just the power transformer.

The Motorola power transformer is a 600 volt center tapped primary, the V-M is 640 volts and the B+ current on both is 170-180 mA, so no problem there. There is a 5-volt/3-amp winding for the 5U4 heater, which is a direct swap.

The custom part for the V-M is not just one but three 6.3v heater windings, not center tapped but with hum controls to float the ground reference for tube heaters in the tuner and in the preamplifier. The Motorola has a single center-tapped winding, connected to all four output tube cathodes, via resistor and cap to ground reference.

Once I dig in, posting both schematics, there may be some work-around.

Under V-M model 812 in the HW Sams Index, it also lists another set and folder besides 499, which does NOT match the transformer schematic.

The V-M model 816 in set 542, also referenced under 812, shows what this console has. I would have to assume V-M did not make as many changes from year to year, carrying over a popular model but with internal modifications. The originally-designed transformer has even more taps to feed a second rectifier 5Y3 , for 130 VDC to the tuner. Any replacement for this highly-custom wound PT, would need to rework the power supply as designed.

Better than finding this is a simpler transformer with only two 6.3v windings and after labeling all the transformer leads with brady tags preparing for a swap... I decided to measure winding resistance and found nothing unusual, then powered it up through a 3 amp fuse.

It was making a tiny bit of noise, still smelling of an overheating event, yet stayed cool drawing only .25 amps unloaded. Leaving it on for an hour last night with the tubes plugged in (minus tuner and preamp that also derive tube heater voltage), it barely got warm. This might just be OK

I got the preamp in the mail last week, so Im going to test the amp properly using a CD player on a set of 15" Jensens, (two sk14 cabinets I return it in two weeks at the Renninger's Kutztown DVHRC swapfest.

For early restoration work, this amp was a good candidate because it's not like some over-crowded RCA's and Zenith's I have suffered through.

The 815 was given to a new owner. The 812 remains